Method for manufacturing outer joint member for constant velocity universal joint, shaft member and outer joint member

ABSTRACT

A method of manufacturing an outer joint member of a constant velocity universal includes forming cup and shaft members of medium carbon steel, preparing, as the cup member, a cup member having cylindrical and bottom portions integrally formed by forging, and a joining end surface formed on an outer surface of the bottom portion after the forging, preparing, as the shaft member, a shaft member having a joining end surface to be joined to the bottom portion of the cup member, and bringing the joining end surfaces of the cup and shaft members into abutment against each other. The method also includes welding the cup and shaft members from an outer side of the cup member to an abutment portion between the cup and shaft members in a radial direction of the cup member.

TECHNICAL FIELD

The present invention relates to a method of manufacturing an outer joint member of a constant velocity universal joint and an outer joint member.

BACKGROUND ART

In a constant velocity universal joint, which is used to construct a power transmission system for automobiles and various industrial machines, two shafts on a driving side and a driven side are coupled to each other to allow torque transmission therebetween, and rotational torque can be transmitted at a constant velocity even when each of the two shafts forms an operating angle. The constant velocity universal joint is roughly classified into a fixed type constant velocity universal joint that allows only angular displacement, and a plunging type constant velocity universal joint that allows both the angular displacement and axial displacement. In a drive shaft configured to transmit power from an engine of an automobile to a driving wheel, for example, the plunging type constant velocity universal joint is used on a differential side (inboard side), and the fixed type constant velocity universal joint is used on a driving wheel side (outboard side).

Irrespective of the plunging type and the fixed type, the constant velocity universal joint includes, as main components, an outer joint member including a cup section having track grooves formed in an inner peripheral surface thereof and engageable with torque transmitting elements, and a shaft section that extends from a bottom portion of the cup section in an axial direction. In many cases, the outer joint member is constructed by integrally forming the cup section and the shaft section by subjecting a rod-like solid blank (bar material) to plastic working such as forging and ironing or processing such as cutting work, heat treatment, and grinding.

Incidentally, as the outer joint member, an outer joint member including a long shaft section (long stem) may sometimes be used. In order to equalize lengths of a right part and a left part of an intermediate shaft, the long stem is used for an outer joint member on the inboard side that corresponds to one side of the drive shaft. The long stem is rotatably supported by a rolling bearing. Although varied depending on vehicle types, the length of the long stem section is approximately from 300 mm to 400 mm in general. In the outer joint member, the long shaft section causes difficulty in integrally forming the cup section and the shaft section with high accuracy. Therefore, there is known an outer joint member in which the cup section and the shaft section are formed as separate members, and both the members are joined through friction press-contact. Such a friction press-contact technology is described in, for example, Patent Document 1.

An overview of the friction press-contact technology for the outer joint member described in Patent Document 1 is described with reference to FIG. 20 and FIG. 21. An intermediate product 71′ of an outer joint member 71 includes a cup member 72 and a shaft member 73, which are joined through the friction press-contact. As illustrated in FIG. 20, burrs 75 are generated in at least one of inner and outer diameter portions on a joining portion 74 along with the press-contact. In order to mount a rolling bearing (see FIG. 1) to a shaft section of the intermediate product 71′ of the outer joint member 71, as illustrated in FIG. 21, it is necessary to remove the burrs 75 on the radially outer side of the joining portion 74 through processing such as turning. Although illustration is omitted, the intermediate product 71′ is processed into a finished product of the outer joint member 71 through machining of a spline, snap ring grooves, and the like, and through heat treatment, grinding, and the like. Therefore, the outer joint member 71 and the intermediate product 71′ have slight differences in shape, but illustration of the slight differences in shape is omitted in FIG. 21 to simplify the description, and the outer joint member 71 being the finished product and the intermediate product 71′ are denoted by the reference symbols at the same parts. The same applies to the description below.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: JP 2012-57696 A

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

The burrs 75 on the joining portion 74 generated due to the friction press-contact described above are quenched by friction heat and cooling that follows the friction heat. Thus, the burrs 75 have a high hardness and a distorted shape extended in a radial direction and an axial direction. Therefore, as illustrated in FIG. 21, when removing the burrs 75 on the radially outer side through the turning, a tip for turning is liable to be significantly abraded due to the high hardness and cracked due to the distorted shape. Therefore, it is difficult to increase the turning speed. In addition, the cutting amount per pass of the tip for turning is decreased, and hence the number of passes is increased, which causes a problem in that the cycle time is increased to increase manufacturing cost.

Further, in order to inspect a joining state of the joining portion 74 of the outer joint member 71, when ultrasonic flaw detection, which enables flaw detection at high speed, is to be performed, an ultrasonic wave is scattered due to the burrs 75 remaining on the radially inner side of the joining portion 74, and hence the joining state cannot be checked. Therefore, there occurs a problem in that total inspection through the ultrasonic flaw detection cannot be performed after the joining.

In view of the above-mentioned problems, when the components are joined through laser welding or electron beam welding, the surfaces of the joining portion may be prevented from being increased in thickness unlike the case of the friction press-contact. However, when the cup member 72 and the shaft member 73 as illustrated in FIG. 22 are brought into abutment against each other to be welded, a gas pressure in a hollow cavity portion 76 is increased due to processing heat during the welding, and after completion of the welding, the pressure is decreased. Due to the variation in the internal pressure of the hollow cavity portion 76, blowing of a molten material occurs. Thus, a recess is formed on radially outer surfaces of the welded portion, poor welding in terms of depth occurs, and air bubbles are generated inside the welded portion, thereby degrading the welding state. As a result, the strength of the welded portion is not stable, which adversely affects quality.

In addition, the cup member 72 and the shaft member 73, which are joined through the friction press-contact as illustrated in FIG. 20 and FIG. 21 or joined by welding as illustrated in FIG. 22 as described above, are joined at an intermediate position on the entire shaft section having a shape and dimensions different for each vehicle type. Accordingly, as described later, it was proved that there is also a problem in terms of cost reduction achieved through enhancement of productivity and standardization of a product type of the cup member.

In addition, the inventors of the present invention have focused on the fact that, in the outer joint member of the constant velocity universal joint being a mass-produced product for automobiles and the like, it is essential to reduce processing steps for the shaft member to enhance productivity and reduce the manufacturing cost.

The present invention has been proposed in view of the above-mentioned problems, and has an object to provide a method of manufacturing an outer joint member and an outer joint member, which are capable of increasing strength of a welded portion and quality, reducing welding cost, enhancing productivity of the shaft member, reducing the manufacturing cost, achieving cost reduction through standardization of a product type, and reducing a burden of production management.

Solutions to the Problems

In order to achieve the above-mentioned object, the inventors of the present invention have diligently conducted research and verification to arrive at the following findings. Based on the findings from multiple aspects, the inventors of the present invention have conceived a novel manufacturing concept in consideration of mass-productivity to achieve the present invention.

(1) In terms of production technology, when the cup member and the shaft member are welded to each other under a state in which the cup member and the shaft member are placed in a sealed space and the hollow cavity portion as well as the sealed space is evacuated, blowing of a molten material and generation of air bubbles are suppressed.

(2) Further, in terms of productivity, when welding is performed on the cup member and the shaft member after being subjected to heat treatment such as quenching and tempering in order to enhance productivity, a temperature of a peripheral portion is increased by heat generated during the welding, which causes a risk of reduction in hardness of a heat-treated portion. To address this problem, the inventors of the present invention have focused on a joining method involving steps capable of achieving highest efficiency and greatest cost reduction without affecting the joint function through change in the order of the welding step. For example, the following steps are adopted. In a case of a cup member and a shaft member having no risk of thermal effect during the welding, the cup member and the shaft member in a finished state after being subjected to heat treatment that involves quenching and tempering are welded to each other. In a case of a cup member and a shaft member having a risk of thermal effect, on the other hand, the cup member and the shaft member are subjected to heat treatment after the welding. As in this example, the inventors of the present invention have found a concept of adopting optimum steps depending on shapes, specifications, and the like of the cup member and the shaft member.

(3) Still further, in terms of productivity and standardization of the product type, the inventors of the present invention have found the following problem with the cup member 72 illustrated in FIG. 20 to FIG. 22. That is, the cup member 72 has a short shaft section formed by forging or the like to have a diameter smaller than that of the bottom portion of the cup section. This short shaft section is prepared based on the shape and dimensions of the shaft member 73, and is joined to the shaft member 73 at an intermediate position on the entire shaft section. Depending on a vehicle to which the shaft member 73 is assembled, the shaft member 73 is required to have a variety of shaft diameters and outer peripheral shapes in addition to differences in types such as a general length stem type and a long stem type. Therefore, when the short shaft section of the cup member 72 is prepared based on the shape and dimensions of the shaft member 73, and is joined to the shaft member 73 at the intermediate position on the entire shaft section, a cup member 72 dedicated to one type of the shaft member 73 is required due to differences both in shaft diameter (joining diameter) and in shape and length (joining position) of the short shaft section of the cup member 72 to be joined to the shaft member 73. Therefore, it was proved that there is a problem also in terms of cost reduction achieved through enhancement of productivity and standardization of a product type of the cup member.

(4) In addition, the inventors of the present invention have found that, in order to practically achieve the novel manufacturing concept for the outer joint member of the constant velocity universal joint being a mass-produced product for automobiles and the like, it is necessary to elaborate forging so that processing steps for the shaft member of the outer joint member can be reduced to enhance productivity and reduce manufacturing cost. Specifically, for example, in forging using an upsetter, a material is conveyed through the steps, and hence a conveyance time cannot be ignored to cause decrease in material temperature. Further, when the number of steps is large, the material is brought into contact with a mold more frequently, and hence the material temperature is liable to be decreased. When the material temperature is decreased, there is a problem in that the material cannot be formed into an intended shape in a predetermined step due to large deformation resistance. Therefore, hitherto, it has been necessary to perform forging by increasing the material temperature to a hot region of from 1,000° C. to 1,200° C. As a result, a crystal grain is liable to be enlarged by being heated to the hot region, which makes it necessary to perform a normalizing step after the forging. Further, in the hot region, an oxide film called a scale is formed on a surface of a forged product, and hence there is a problem of increase in manufacturing cost caused by necessity of a shot-peening step. In particular, a long shaft product has no cost advantage as compared to turning of an entire region from a bar material. Therefore, the processing by forging tends to be avoided.

As a technical measure to achieve the above-mentioned object, according to one embodiment of the present invention, there is provided a method of manufacturing an outer joint member of a constant velocity universal joint, which is constructed by forming, through use of separate members, a cup section having track grooves formed at an inner periphery of the cup section and engageable with torque transmitting elements, and a shaft section formed at a bottom portion of the cup section, and by welding a cup member forming the cup section and a shaft member forming the shaft section, the method comprising: forming the cup member and the shaft member of medium carbon steel; preparing, as the cup member, a cup member having a cylindrical portion and a bottom portion integrally formed by forging, and a joining end surface formed on an outer surface of the bottom portion in a machining step after the forging; preparing, as the shaft member, a shaft member having a joining end surface to be joined to the bottom portion of the cup member, which is formed in the machining step; bringing the joining end surface of the cup member and the joining end surface of the shaft member into abutment against each other; and welding the cup member and the shaft member by radiating a beam from an outer side of the cup member to an abutment portion between the cup member and the shaft member in a radial direction of the cup member, wherein the shaft member has a step portion in which the joining end surface is formed and a radially inner side recessed portion formed thereon by forging from a billet cut from a bar material.

Further, according to one embodiment of the present invention for an outer joint member, there is provided an outer joint member of a constant velocity universal joint, comprising: a cup section having track grooves formed at an inner periphery of the cup section and engageable with torque transmitting elements; and a shaft section formed at a bottom portion of the cup section, the outer joint member being constructed by forming the cup section and the shaft section through use of separate members, and by welding a cup member forming the cup section and a shaft member forming the shaft section, the cup member and the shaft member being formed of medium carbon steel, the cup member having a cylindrical portion and a bottom portion integrally formed by forging, and a joining end surface formed on an outer surface of the bottom portion, the shaft member having a joining end surface formed at an end portion of the shaft member to be joined to the bottom portion of the cup member, the cup member and the shaft member being welded to each other under a state in which the joining end surface of the cup member and the joining end surface of the shaft member are held in abutment against each other, the outer joint member comprising a welded portion between the cup member and the shaft member, which is formed of a bead formed by a beam radiated in a radial direction of the cup member from an outer side of the cup member, the shaft member having a recessed portion formed on a radially inner side of the joining end surface, the recessed portion having a surface formed by forging.

With the above-mentioned configuration, it is possible to achieve the method of manufacturing an outer joint member and the outer joint member, which are capable of increasing strength of a welded portion and quality, reducing welding cost, enhancing productivity of the shaft member, reducing the manufacturing cost, achieving cost reduction through standardization of a product type, and reducing a burden of production management.

Specifically, when the outer diameter of the joining end surface is set to an equal dimension for each joint size, a degree of processing for the cup member to be standardized in product type can be increased. As a result, the enhancement of productivity and reducing the burden of production management can be further promoted.

In this case, in Claims and Specification of the present invention, setting the outer diameter of the joining end surface of the cup member to an equal dimension for each joint size is not limited to preparing one type of the cup member for one joint size, that is, not limited to preparing the cup member assigned with a single product number. For example, the present invention encompasses preparing cup members of a plurality of types (assigned with a plurality of product numbers, respectively) for one joint size based on different specifications of a maximum operating angle, and setting the outer diameter of the joining end surface of each of the cup members to an equal dimension. In addition, the present invention encompasses, for example, preparing cup members of a plurality of types (assigned with a plurality of product numbers, respectively) for one joint size in order to achieve management of the cup members in a plurality of forms including intermediate components before heat treatment and finished components after heat treatment in consideration of the joint function, the circumstances at the manufacturing site, the productivity, and the like, and setting the outer diameter of the joining end surface of each of the cup members to an equal dimension.

However, the outer diameter of the joining end surface of the cup member and the outer diameter of the joining end surface of the shaft member need not be set to equal dimensions. In consideration of, for example, a state of the weld bead, a dimensional difference may be given as appropriate in such a manner that the outer diameter of the joining end surface of the shaft member is set slightly smaller than the outer diameter of the joining end surface of the cup member, or that the outer diameter of the joining end surface of the shaft member is set slightly larger than the outer diameter of the joining end surface of the cup member, conversely. The description “the outer diameters of the joining end surfaces of the cup member and the shaft member are set to equal dimensions for each joint size” herein refers to a concept encompassing a case where the dimensional difference is given as appropriate between the outer diameter of the joining end surface of the cup member and the outer diameter of the joining end surface of the shaft member.

Further, in Claims and Specification of the present invention, setting the outer diameter of the joining end surface to an equal dimension for each joint size, and forming a protruding surface into the same shape for each joint size may be applied also to different types of constant velocity universal joints. For example, the present invention encompasses setting outer diameters of the joining end surfaces of a tripod type constant velocity universal joint and a double-offset constant velocity universal joint to equal dimensions on the inboard side, and encompasses setting outer diameters of the joining end surfaces of a Rzeppa type constant velocity universal joint and an undercut-free type constant velocity universal joint to equal dimensions on the outboard side. Further, the present invention also encompasses setting the outer diameters of the joining end surfaces of the constant velocity universal joints on the inboard side and the outboard side to equal dimensions on the inboard side and the outboard side.

It is preferred that the forging of the shaft member comprise a preforming step of forming the step portion in which the joining end surface is formed from the billet into a tapered shape, and a main forming step of forming the step portion in which the joining end surface is formed and the recessed portion. With this, the number of steps is reduced, and forging at a heating temperature in a temperature region lower than the hot region can be performed.

It is preferred that a ratio L2/Dw2 of an upset distance (L2) in the main forming step and a diameter (Dw2) after the preforming be set to be smaller than a ratio L1/Dw1 of an upset distance (L1) in the preforming step and a diameter (Dw1) of the billet. With this, the occurrence of buckling is prevented, and stable upsetting is enabled, for example, without roll-in of a surface.

When the billet is formed with a punch having a conical angle (θ) of from 5° to 20° in the preforming step, bucking can be prevented even at a heating temperature in the temperature region lower than the hot region.

When the billet is heated to a temperature of from 800° C. to 1,000° C. in the forging of the shaft member, the normalizing step and the shot-peening step after the forging can be omitted to enhance productivity of the shaft member and reduce the manufacturing cost.

When the central segregated portion of the billet is fastened in the recessed portion, an outer joint member of a constant velocity universal joint having satisfactory strength of a welded portion and satisfactory quality is obtained.

Effects of the Invention

According to the method of manufacturing an outer joint member of a constant velocity universal joint and the outer joint member of the present invention, it is possible to achieve the method of manufacturing an outer joint member and the outer joint member, which are capable of increasing the strength of the welded portion and the quality, reducing the welding cost, enhancing productivity of the shaft member, reducing the manufacturing cost, achieving the cost reduction through the standardization of a product type of the cup member, and reducing the burden of production management.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view for illustrating the entire structure of a drive shaft to which an outer joint member according to a first embodiment of the present invention is applied.

FIG. 2a is an enlarged partial vertical sectional view for illustrating the outer joint member of FIG. 1.

FIG. 2b is an enlarged view for illustrating a welded portion.

FIG. 2c is an enlarged view for illustrating a shape before welding.

FIG. 3 is a diagram for illustrating an overview of manufacturing steps for the outer joint member of FIG. 1.

FIG. 4a is a vertical sectional view for illustrating a cup member before welding and after ironing.

FIG. 4b is a vertical sectional view for illustrating the cup member before welding and after turning.

FIG. 5a is a front view for illustrating a shaft member before welding, that is, a billet obtained by cutting a bar material.

FIG. 5b is a partial vertical sectional view for illustrating the shaft member before welding and after forging.

FIG. 5c is a partial vertical sectional view for illustrating the shaft member before welding and after turning and spline processing.

FIG. 6a is a vertical sectional view for illustrating a preforming step in forging of the shaft member.

FIG. 6b is an enlarged vertical sectional view for illustrating a preformed product in the forging of the shaft member.

FIG. 7 is a vertical sectional view for illustrating a main forming step.

FIG. 8 is a vertical sectional view for illustrating forging lines.

FIG. 9 is a vertical sectional view for illustrating findings in the course of development.

FIG. 10 is a view for illustrating an overview of a welding step.

FIG. 11 is a view for illustrating an overview of the welding step.

FIG. 12 is a front view for illustrating a shaft member assigned with a different product number.

FIG. 13 is a partial vertical sectional view for illustrating an outer joint member that is manufactured using the shaft member illustrated in FIG. 12.

FIG. 14 is a diagram for illustrating an example of standardization of a product type of the cup member.

FIG. 15 is a vertical sectional view for illustrating a modified example of a cup member according to the first embodiment.

FIG. 16 is a diagram for illustrating an overview of a method of manufacturing an outer joint member according to a second embodiment of the present invention.

FIG. 17 is a diagram for illustrating an overview of a method of manufacturing an outer joint member according to a third embodiment of the present invention.

FIG. 18 is a partial vertical sectional view for illustrating a constant velocity universal joint using an outer joint member according to the second embodiment of the present invention.

FIG. 19 is a partial vertical sectional view for illustrating the outer joint member of FIG. 18.

FIG. 20 is a vertical sectional view for illustrating an outer joint member according to a related art.

FIG. 21 is a vertical sectional view for illustrating the outer joint member according to the related art.

FIG. 22 is a vertical sectional view for illustrating an outer joint member according to a related art.

EMBODIMENTS OF THE INVENTION

Now, description is made of embodiments of the present invention with reference to the drawings.

FIG. 3 to FIG. 14 are illustrations of a method of manufacturing an outer joint member of a constant velocity universal joint according to a first embodiment of the present invention, and FIG. 1 and FIG. 2 are illustrations of an outer joint member according to the first embodiment of the present invention. First, the outer joint member according to the first embodiment is described with reference to FIG. 1 and FIG. 2, and subsequently, the method of manufacturing an outer joint member according to the first embodiment is described with reference to FIG. 3 to FIG. 14.

FIG. 1 is a view for illustrating the entire structure of a drive shaft 1 using an outer joint member 11 according to the first embodiment. The drive shaft 1 mainly comprises a plunging type constant velocity universal joint 10 arranged on a differential side (right side of FIG. 1: hereinafter also referred to as “inboard side”), a fixed type constant velocity universal joint 20 arranged on a driving wheel side (left side of FIG. 1: hereinafter also referred to as “outboard side”), and an intermediate shaft 2 configured to couple both the constant velocity universal joints 10 and 20 to allow torque transmission therebetween.

The plunging type constant velocity universal joint 10 illustrated in FIG. 1 is a so-called double-offset type constant velocity universal joint (DOJ). The constant velocity universal joint 10 comprises the outer joint member 11 comprising a cup section 12 and a long shaft section (hereinafter referred to also as “long stem section”) 13 that extends from a bottom portion of the cup section 12 in an axial direction, an inner joint member 16 housed along an inner periphery of the cup section 12 of the outer joint member 11, balls 41 serving as torque transmitting elements that are arranged between track grooves 30 and 40 of the outer joint member 11 and the inner joint member 16, and a cage 44 having a spherical outer peripheral surface 45 and a spherical inner peripheral surface 46 that are fitted to a cylindrical inner peripheral surface 42 of the outer joint member 11 and a spherical outer peripheral surface 43 of the inner joint member 16, respectively, and being configured to retain the balls 41. A curvature center O₁ of the spherical outer peripheral surface 45 and a curvature center O₂ of the spherical inner peripheral surface 46 of the cage 44 are offset equidistantly from a joint center O toward opposite sides in the axial direction.

An inner ring of a support bearing 6 is fixed to an outer peripheral surface of the long stem section 13, and an outer ring of the support bearing 6 is fixed to a transmission case with a bracket (not shown). The outer joint member 11 is supported by the support bearing 6 in a freely rotatable manner, and when the support bearing 6 as described above is provided, vibration of the outer joint member 11 during driving or the like is prevented as much as possible.

The fixed type constant velocity universal joint 20 illustrated in FIG. 1 is a so-called Rzeppa type constant velocity universal joint, and comprises an outer joint member 21 comprising a bottomed cylindrical cup section 21 a and a shaft section 21 b that extends from a bottom portion of the cup section 21 a in the axial direction, an inner joint member 22 housed along an inner periphery of the cup section 21 a of the outer joint member 21, balls 23 serving as torque transmitting elements that are arranged between the cup section 21 a of the outer joint member 21 and the inner joint member 22, and a cage 24, which is arranged between an inner peripheral surface of the cup section 21 a of the outer joint member 21 and an outer peripheral surface of the inner joint member 22, and is configured to retain the balls 23. As the fixed type constant velocity universal joint 20, an undercut-free type constant velocity universal joint may sometimes be used.

The intermediate shaft 2 comprises splines 3 for torque transmission (including serrations; the same applies hereinafter) at outer peripheries both end portions thereof. The spline 3 on the inboard side is spline-fitted to a hole portion of the inner joint member 16 of the plunging type constant velocity universal joint 10. Thus, the intermediate shaft 2 and the inner joint member 16 of the plunging type constant velocity universal joint 10 are coupled to each other to allow torque transmission therebetween. Further, the spline 3 on the outboard side is spline-fitted to a hole portion of the inner joint member 22 of the fixed type constant velocity universal joint 20. Thus, the intermediate shaft 2 and the inner joint member 22 of the fixed type constant velocity universal joint 20 are coupled to each other to allow torque transmission therebetween. Although the solid intermediate shaft 2 is illustrated, a hollow intermediate shaft may be used instead.

Grease is sealed inside both the constant velocity universal joints 10 and 20 as a lubricant. To prevent leakage of the grease to an outside of the joint or entry of a foreign matter from the outside of the joint, bellows boots 4 and 5 are respectively mounted to a portion between the outer joint member 11 of the plunging type constant velocity universal joint 10 and the intermediate shaft 2 and a portion between the outer joint member 21 of the fixed type constant velocity universal joint 20 and the intermediate shaft 2.

The outer joint member according to the first embodiment is described with reference to FIG. 2. FIG. 2 are enlarged views for illustrating the outer joint member 11 according to this embodiment. FIG. 2a is a partial vertical sectional view. FIG. 2b is an enlarged view for illustrating a portion “A” of FIG. 2a . FIG. 2c is a view for illustrating a shape before welding. The outer joint member 11 comprises the bottomed cylindrical cup section 12 that is opened at one end and has the cylindrical inner peripheral surface 42 and the plurality of track grooves 30, on which the balls 41 (see FIG. 1) are caused to roll, formed equiangularly on the inner peripheral surface, and the long stem section 13 that extends from the bottom portion of the cup section 12 in the axial direction and comprises a spline Sp serving as a torque transmitting coupling portion formed at an outer periphery on an end portion thereof on an opposite side to the cup section 12. In this embodiment, the outer joint member 11 is formed by welding a cup member 12 a and a shaft member 13 a to each other.

The cup member 12 a illustrated in FIG. 2a to FIG. 2c is an integrally-formed product being made of medium carbon steel, such as S53C, containing carbon of from 0.40 wt % to 0.60 wt %, and having a cylindrical portion 12 a 1 and a bottom portion 12 a 2. The cylindrical portion 12 a 1 has the track grooves 30 and the cylindrical inner peripheral surface 42 formed at an inner periphery thereof. A projecting portion 12 a 3 is formed at the bottom portion 12 a 2 of the cup member 12 a. A boot mounting groove 32 is formed at an outer periphery of the cup member 12 a on the opening side thereof, whereas a snap ring groove 33 is formed at an inner periphery of the cup member 12 a on the opening side thereof. A bearing mounting surface 14 and a snap ring groove 15 are formed at an outer periphery of the shaft member 13 a on the cup member 12 a side, whereas the spline Sp is formed at an end portion of the shaft member 13 a on an opposite side.

The shaft member 13 a is made of medium carbon steel, such as S40C, containing carbon of from 0.30 wt % to 0.55 wt %. A joining end surface 50 formed at the projecting portion 12 a 3 of the bottom portion 12 a 2 of the cup member 12 a and a joining end surface 51 formed at an end portion of the shaft member 13 a on the cup member 12 a side are brought into abutment against each other, and are welded to each other by electron beam welding performed from an outer side of the cup member 12 a in a radial direction. As illustrated in FIG. 2a and FIG. 2b , a welded portion 49 is formed of a bead, which is formed by a beam radiated from a radially outer side of the cup member 12 a. Although detailed description is made later, outer diameters B of the joining end surface 50 and the joining end surface 51 (see FIG. 4b and FIG. 5c ) are set to equal dimensions for each joint size. However, the outer diameter B of the joining end surface 50 of the cup member 12 a and the outer diameter B of the joining end surface 51 of the shaft member 13 a need not be set to equal dimensions. In consideration of, for example, a state of the weld bead, a dimensional difference may be given as appropriate in such a manner that the outer diameter B of the joining end surface 51 is set slightly smaller than the outer diameter B of the joining end surface 50, or that the outer diameter B of the joining end surface 51 is set slightly larger than the outer diameter B of the joining end surface 50, conversely. The description “the outer diameters B of the joining end surface 50 and the joining end surface 51 are set to equal dimensions for each joint size” herein refers to a concept encompassing a case where the dimensional difference is given as appropriate between the outer diameter B of the joining end surface 50 and the outer diameter B of the joining end surface 51.

As illustrated in FIG. 2a , the welded portion 49 is formed on the joining end surface 51 located on the cup member 12 a side with respect to the bearing mounting surface 14 of the shaft member 13 a, and hence the bearing mounting surface 14 and the like can be processed in advance so that post-processing after welding can be omitted. Further, due to the electron beam welding, burrs are not generated at the welded portion. Thus, post-processing for the welded portion can also be omitted, which can reduce manufacturing cost. Still further, total inspection on the welded portion through ultrasonic flaw detection can be performed.

As illustrated in FIG. 2c , the joining end surface 50 of the cup member 12 a is formed by annular turning, and a center portion in a radial direction maintains a forged surface. With this, a turning time is shortened.

Next, the manufacturing method according to the first embodiment of the present invention is described with reference to FIG. 3 to FIG. 14. Before description of details of the features of the manufacturing method of this embodiment, that is, forging of the shaft member, an overview of manufacturing steps (processing steps) is described. FIG. 3 is an illustration of the overview of the manufacturing steps for the outer joint member. In this embodiment, as illustrated in FIG. 3, the cup member 12 a is manufactured through manufacturing steps comprising a bar material cutting step S1 c, a forging step S2 c, an ironing step S3 c, and a turning step S4 c. Meanwhile, the shaft member 13 a is manufactured through manufacturing steps comprising a bar material cutting step S1 s, a forging step S2 s, a turning step S3 s, and a spline processing step S4 s. Intermediate components of the cup member 12 a and the shaft member 13 a thus manufactured are each assigned with a product number for management.

After that, the cup member 12 a and the shaft member 13 a are subjected to a welding step S6, a heat treatment step S7, and a grinding step S8 so that the outer joint member 11 is completed. A machining step described in Claims refers to the turning step S4 c and the turning step S3 s among the above-mentioned manufacturing steps, and to a grinding step S6 s described later (see FIG. 17).

An overview of each step is described. Each step is described as a typical example, and appropriate modification and addition may be made to each step as needed. First, the manufacturing steps for the cup member 12 a are described.

[Bar Material Cutting Step S1 c]

A bar material is cut into a predetermined length in accordance with a forging weight, thereby producing a billet.

[Forging Step S2 c]

The billet is subjected to forging so as to integrally form the cylindrical portion, the bottom portion, and the projecting portion as a preform of the cup member 12 a.

[Ironing Step S3 c]

Ironing is performed on the track grooves 30 and the cylindrical inner peripheral surface 42 of the preform, thereby finishing the inner periphery of the cylindrical portion of the cup member 12 a.

[Turning Step S4 c]

In the preform after ironing, the outer peripheral surface, the boot mounting groove 32, the snap ring groove 33 and the like, and the joining end surface 50 are formed by turning. In this embodiment, after the turning step S4 c, the cup member 12 a in the form of an intermediate component is assigned with a product number for management.

Next, the manufacturing steps for the shaft member 13 a are described.

[Bar Material Cutting Step S1 s]

A bar material is cut into a predetermined length in accordance with the forging weight, thereby producing a billet.

[Forging Step S2 s]

After that, the billet is forged into a rough shape by upset forging depending on the shape of the shaft member 13 a.

[Turning Step S3 s]

The outer peripheral surface of the billet (bearing mounting surface 14, snap ring groove 15, minor diameter of the spline, end surface, and the like) and the joining end surface 51 of the billet at the end portion on the cup member 12 a side are formed by turning.

[Spline Processing Step S4 s]

The spline is formed by rolling in the shaft member after turning. Note that, the method of forming the spline is not limited to the rolling, and press working or the like may be adopted instead as appropriate. In this embodiment, after the spline processing, the shaft member 13 a in the form of an intermediate component is assigned with a product number for management.

Next, the manufacturing steps in the process of completing the outer joint member 11 from the cup member 12 a and the shaft member 13 a are described.

[Welding Step S6]

The joining end surface 50 of the cup member 12 a and the joining end surface 51 of the shaft member 13 a are brought into abutment against each other and welded. After the welding, the welded portion 49 between the cup member 12 a and the shaft member 13 a is inspected by the ultrasonic flaw-detection method.

[Heat Treatment Step S7]

Induction quenching and tempering are performed as heat treatment on at least the track grooves 30 and the cylindrical inner peripheral surface 42 of the cup section 12 after welding and a necessary range of the outer periphery of the shaft section 13 after welding. Heat treatment is not performed on the welded portion. A hardened layer having a hardness of approximately from 58 HRC to 62 HRC is formed on each of the track grooves 30 and the cylindrical inner peripheral surface 42 of the cup section 12. Further, a hardened layer having a hardness of approximately from 50 HRC to 62 HRC is formed in a predetermined range of the outer periphery of the shaft section 13.

[Grinding Step S8]

After the heat treatment, the bearing mounting surface 14 of the shaft section 13 and the like are finished by grinding. Thus, the outer joint member 11 is completed.

In the manufacturing steps of this embodiment, the heat treatment step is provided after the welding step, and hence the manufacturing steps are suited to a cup member and a shaft member having such shapes and specifications that the hardness of the heat-treated portion may be affected by temperature rise at the periphery due to heat generated during the welding.

Next, main constituent features of the manufacturing method of this embodiment are described in detail. FIG. 4a is a vertical sectional view for illustrating a state after ironing of the cup member 12 a. FIG. 4b is a vertical sectional view for illustrating a state after turning. In a preform 12 a′ for the cup member 12 a, a cylindrical portion 12 a 1′, a bottom portion 12 a 2′, and a projecting portion 12 a 3′ are integrally formed in the forging step S2 c. After that, the track grooves 30 and the cylindrical inner peripheral surface 42 are formed by ironing in the ironing step S3 c so that the inner periphery of the cylindrical portion 12 a 1′ is finished as illustrated in FIG. 4 a.

After that, in the turning step S4 c, the outer peripheral surface, the boot mounting groove 32, the snap ring groove 33, and the like of the cup member 12 a as well as the joining end surface 50 of the projecting portion 12 a 3 of the bottom portion 12 a 2 and the joining end surface 50 having the the outer diameter B are formed by turning as illustrated in FIG. 4 b.

FIG. 5 are illustrations of states of the shaft member 13 a in the respective processing steps. FIG. 5a is a front view for illustrating a billet 13 a″ obtained by cutting a bar material. FIG. 5b is a partial vertical sectional view for illustrating a preform 13 a′ obtained by forging the billet 13 a″ into a rough shape by the forging (upset forging). FIG. 5c is a partial vertical sectional view for illustrating the shaft member 13 a after turning and spline processing.

The billet 13 a″ illustrated in FIG. 5a is produced in the bar material cutting step S1 s. In the forging step S2 s, the preform 13 a′ is produced by increasing the shaft diameter of the billet 13 a″ in a predetermined range and forming a recessed portion 52 at a joining-side end portion (end portion on the cup member 12 a side) while forming a step portion 54 in which the joining end surface 51 is formed, a second step portion 55 in which the bearing mounting surface 14 is formed, and a first step portion 56 by upset forging as illustrated in FIG. 5 b.

After that, in the turning step S3 s, the outer diameter portion of the shaft member 13 a, the bearing mounting surface 14, the snap ring groove 15, an inner diameter portion 53 (inner diameter E) of the recessed portion 52, and the joining end surface 51 having the outer diameter B are formed by turning as illustrated in FIG. 5c . In the spline processing step S4 s, the spline Sp is processed at the end portion on the opposite side to the recessed portion 52 by rolling or press forming.

The outer diameter B of the joining end surface 50 located at the projecting portion 12 a 3 of the bottom portion 12 a 2 of the cup member 12 a illustrated in FIG. 4b is set to an equal dimension for one joint size. Further, in the shaft member 13 a illustrated in FIG. 5c , which is used as a long stem shaft, the outer diameter B of the joining end surface 51 located at the end portion on the cup member 12 a side is set to an equal dimension to the outer diameter B of the joining end surface 50 of the cup member 12 a irrespective of the shaft diameter and the outer peripheral shape. Still further, the joining end surface 51 of the shaft member 13 a is located at the position on the cup member 12 a side with respect to the bearing mounting surface 14. Through the setting of dimensions as described above, the outer joint member 11 compatible with various vehicle types can be manufactured in such a manner that, while the cup member 12 a is prepared for common use, only the shaft member 13 a is manufactured to have a variety of shaft diameters, lengths, and outer peripheral shapes depending on vehicle types, and both the members 12 a and 13 a are welded to each other. Details of the preparation of the cup member 12 a for common use are described later.

Next, a method of welding the cup member 12 a and the shaft member 13 a is described with reference to FIG. 10 and FIG. 11. FIG. 10 and FIG. 11 are views for illustrating an overview of a welding apparatus. FIG. 10 is an illustration of a state before welding. FIG. 11 is an illustration of a state during welding. As illustrated in FIG. 10, a welding apparatus 100 mainly comprises an electron gun 101, a rotation device 102, a chuck 103, a center hole guide 104, a tailstock 105, workpiece supports 106, a center hole guide 107, a case 108, and a vacuum pump 109.

The cup member 12 a and the shaft member 13 a being workpieces are placed on the workpiece supports 106 arranged inside the welding apparatus 100. The chuck 103 and the center hole guide 107 arranged at one end of the welding apparatus 100 are coupled to the rotation device 102. The chuck 103 grips the cup member 12 a to rotate the cup member 12 a under a state in which the cup member 12 a is centered by the center hole guide 107. The center hole guide 104 is integrally mounted to the tailstock 105 arranged at another end of the welding apparatus 100. Both the center hole guide 104 and the tailstock 105 are configured to reciprocate in the axial direction (lateral directions of FIG. 10 and FIG. 11).

A center hole of the shaft member 13 a is set on the center hole guide 104 so that the shaft member 13 a is centered. The vacuum pump 109 is connected to the case 108 of the welding apparatus 100. A “sealed space” herein refers to a space 111 defined by the case 108. In this embodiment, the cup member 12 a and the shaft member 13 a are entirely received in the sealed space 111. The electron gun 101 is arranged at a position corresponding to the joining end surfaces 50 and 51 of the cup member 12 a and the shaft member 13 a. The electron gun 101 is configured to approach the workpieces up to a predetermined position.

Next, the operation of the welding apparatus 100 constructed as described above and the welding method are described. The cup member 12 a and the shaft member 13 a being workpieces are stocked at a place different from the place of the welding apparatus 100. The respective workpieces are taken out by, for example, a robot, are conveyed into the case 108 of the welding apparatus 100 opened to the air as illustrated in FIG. 10, and are set at predetermined positions on the workpiece supports 106. At this time, the center hole guide 104 and the tailstock 105 are retreated to the right side of FIG. 6, and hence a gap is formed between the joining end surfaces 50 and 51 of the cup member 12 a and the shaft member 13 a. After that, a door (not shown) of the case 108 is closed, and the vacuum pump 109 is activated to reduce the pressure in the sealed space 111 defined in the case 108. Thus, the pressures in the recessed portion 52 and the inner diameter portion 53 of the shaft member 13 a are reduced as well.

When the pressure in the sealed space 111 is reduced to a predetermined pressure, the center hole guide 104 and the tailstock 105 are advanced to the left side as illustrated in FIG. 11 to eliminate the gap between the joining end surfaces 50 and 51 of the cup member 12 a and the shaft member 13 a. Thus, the cup member 12 a is centered by the center hole guide 107 and fixed by the chuck 103, whereas the shaft member 13 a is supported by the center hole guide 104. After that, the workpiece supports 106 are moved away from the workpieces. At this time, the distance between the workpiece supports 106 and the workpieces may be infinitesimal, and hence illustration of this distance is omitted from FIG. 11. As a matter of course, the welding apparatus 100 may have such a structure that the workpiece supports 106 are retreated downward greatly.

Although illustration is omitted, the electron gun 101 is then caused to approach the workpieces up to a predetermined position, and the workpieces are rotated to start pre-heating. As a pre-heating condition, unlike the welding condition, the temperature is set lower than the welding temperature by, for example, radiating an electron beam under a state in which the electron gun 101 is caused to approach the workpieces so as to increase the spot diameter. Through the pre-heating, the cooling rate after welding is reduced, thereby being capable of preventing a quenching crack. When a predetermined pre-heating time has elapsed, the electron gun 101 is retreated to a predetermined position, and radiates the electron beam from the outer side of the workpieces in the radial direction to start welding. When the welding is finished, the electron gun 101 is retreated, and the rotation of the workpieces is stopped.

Although illustration is omitted, the sealed space 111 is then opened to the air. Then, under a state in which the workpiece supports 106 are raised to support the workpieces, the center hole guide 104 and the tailstock 105 are retreated to the right side, and the chuck 103 is opened. After that, for example, the robot grips the workpieces, takes the workpieces out of the welding apparatus 100, and places the workpieces into alignment on a cooling stocker. In this embodiment, the cup member 12 a and the shaft member 13 a are entirely received in the sealed space 111, and hence the configuration of the sealed space 111 defined in the case 108 can be simplified.

Specifically, the cup member 12 a having a carbon content of from 0.4% to 0.6% and the shaft member 13 a having a carbon content of from 0.3% to 0.55% were used and welded to each other in the above-mentioned welding apparatus 100 under the condition that the pressure in the sealed space 111 defined in the case 108 was set to 6.7 Pa or less. In order to prevent the cup member 12 a and the shaft member 13 a from being cooled rapidly after the welding to suppress increase in hardness of the welded portion, the joining end surfaces 50 and 51 of the cup member 12 a and the shaft member 13 a were soaked by pre-heating to have a temperature of from 300° C. to 650° C., and then electron beam welding was performed. As a result, a welded portion having a projecting height from the welded surface (0.5 mm or less), which imposed no adverse effect on a product function, was obtained. Further, through the soaking by pre-heating, the hardness of the welded portion after completion of the welding was able to be kept within a range of from 200 Hv to 500 Hv, thereby being capable of attaining high welding strength and stable welding state and quality. Still further, the cup member 12 a and the shaft member 13 a were welded to each other under the condition that the pressure in the sealed space 111 of the welding apparatus 100 was set to an atmospheric pressure or less, thereby being capable of suppressing the change in pressure in the hollow cavity portion during the welding. As a result, the blowing of a molten material and the entry of the molten material toward the radially inner side were able to be prevented.

The overview of the manufacturing steps (processing steps) of this embodiment is as described above. Next, the forging step for the shaft member being the feature of this embodiment is described with reference to FIG. 6 to FIG. 9. FIG. 6 are illustrations of the forging of the shaft member. FIG. 6a is a vertical sectional view for illustrating a preforming step. FIG. 6b is an enlarged vertical sectional view for illustrating a preformed product. FIG. 7 is a vertical sectional view for illustrating a main forming step. FIG. 8 is a vertical sectional view for illustrating forging lines. FIG. 9 is a vertical sectional view for illustrating findings in the course of development.

Hitherto, it has been necessary to perform forging by increasing the material temperature to the hot region of from 1,000° C. to 1,200° C. due to a problem in that deformation resistance is increased by decrease in material temperature. As a result, a crystal grain is liable to be enlarged by being heated to the hot region, which makes it necessary to perform a normalizing step after the forging. Further, in the hot region, an oxide film called a scale is formed on a surface of a forged product, and hence there is a problem of increase in manufacturing cost caused by necessity of a shot-peening step. This problem is solved by the forging step S2 s for the shaft member of this embodiment.

Specifically, in the forging step S2 s for the shaft member of this embodiment, a condition described later is derived through an evaluation test, with the result that the forging can be performed in the temperature region of from 800° C. to 1,000° C. lower than the hot region in the number of steps (2 to 3 steps) in which the forging can be performed before decrease in material temperature.

First, an overview of the forging step S2 s for the shaft member is described. In this embodiment, upset forging was performed through use of an upsetter. The forging step S2 s comprises the preforming step and the main forming step. As illustrated in FIG. 6a , a mold in the preforming step mainly comprises a die 120 and a punch 121. An upper half from a center line of the billet 13 a″ of FIG. 6a represents a state before the preforming, and a lower half thereof represents a state after the preforming. The die 120 is halved into upper and lower portions, and an inner peripheral surface thereof comprises a cylindrical inner peripheral surface 120 a having a diameter that is substantially equal to a diameter Dw1 of the billet 13 a″, a first step portion forming surface 120 b having a diameter larger than the diameter of the cylindrical inner peripheral surface 120 a, and a second step portion forming surface 120 c having a diameter further larger than the diameter of the first step portion forming surface 120 b. A connected portion 120 d between the cylindrical inner peripheral surface 120 a and the first step portion forming surface 120 b is smoothly formed into a tapered shape with roundness. Similarly, a connected portion 120 e between the first step portion forming surface 120 b and the second step portion forming surface 120 c is also smoothly formed into a tapered shape with roundness. The first step portion forming surface 120 b and the second step portion forming surface 120 c are formed into a substantially cylindrical shape.

Meanwhile, an inner peripheral surface of the punch 121 comprises a tapered forming surface 121 a having a conical angle θ. A bottom portion of the forming surface 121 a has a diameter that is substantially equal to the diameter Dw1 of the billet 13 a″.

As illustrated in FIG. 7, a mold in the forming step mainly comprises a die 122 and a punch 123. In FIG. 7, as in FIG. 6a , an upper half from a center line represents a state before the main forming, and a lower half represents a state after the main forming. An inner peripheral surface of the die 122 comprises a cylindrical inner peripheral surface 122 a having a diameter that is substantially equal to the diameter Dw1 of the billet 13 a″, a first step portion forming surface 122 b having a diameter larger than the diameter of the cylindrical inner peripheral surface 122 a, and a second step portion forming surface 122 c having a diameter further larger than the diameter of the first step portion forming surface 122 b. A connected portion 122 d between the cylindrical inner peripheral surface 122 a and the first step portion forming surface 122 b is smoothly formed into a tapered shape with roundness. Similarly, a connected portion 122 e between the first step portion forming surface 122 b and the second step portion forming surface 122 c is also smoothly formed into a tapered shape with roundness. The first step portion forming surface 122 b and the second step portion forming surface 122 c are formed into a substantially cylindrical shape. A second step portion formed by the second step portion forming surface 122 c serves as a portion forming the bearing mounting surface 14. In this embodiment, as the die 122 in the main forming step, the same die as the die 120 in the preforming step is used. However, the present invention is not limited thereto, and both the dies 120 and 122 may be appropriately set to different specifications.

An inner peripheral surface of the punch 123 in the main forming step comprises a substantially cylindrical forming surface 123 a having a slight clearance angle. A step portion formed by the forming surface 123 a serves as a portion forming a joining end surface. A bottom portion of the forming surface 123 a comprises a recessed portion forming surface 123 b configured to form the recessed portion 52.

Next, the forming step using the above-mentioned mold is described. A processed portion of the billet 13 a″ and an unprocessed portion adjacent to the processed portion are heated to a predetermined temperature (from 800° C. to 1,000° C., for example, 900° C.). In the preforming step, as represented by the upper half of FIG. 6a , the heated billet 13 a″ is gripped by the cylindrical inner peripheral surface 120 a of the die 120. Then, the punch 121 advances to pressurize the billet 13 a″ and moves by an upset distance L1. The billet 13 a″ With this, as illustrated in FIG. 6a , the material is filled along the first step portion forming surface 120 b of the die 120, and a preformed product 13 a″1 is formed, which increases in diameter up to a state following a part (connected portion 120 e side) of the second step portion forming surface 120 c and which is gently tapered from the diameter increased portion toward the punch 121 side.

The shape of the preformed product 13 a″1 is illustrated in FIG. 6b . As illustrated in FIG. 6b , the portion that increases in diameter up to a state following the part (connected portion 120 e side) of the second step portion forming surface 120 c has a maximum diameter Dw2″, and a tip end on the punch 121 side has a minimum diameter Dw2′.

Next, the main forming step is described. As represented by the upper half of FIG. 7, the preformed product 13 a″1 is gripped by the cylindrical inner peripheral surface 122 a of the die 122 in the main forming step. Then, the punch 123 advances to pressurize the preformed product 13 a″1 and moves by an upset distance L2. With this, the material is filled along the second step portion forming surface 122 c of the die 122, and the substantially cylindrical forming surface 123 a and the recessed portion forming surface 123 b of the punch 123, to thereby complete a main formed product (preform after the forging) 13 a′.

In the above-mentioned forming step, a central segregated portion of the billet 13 a″ cut from a bar material is fastened in the portion of the minimum diameter Dw2′ at the tip end of the preformed product 13 a″1 on the punch 121 side, and in the main forming step after the preforming step, the central segregated portion is fastened in the recessed portion 52. This state is additionally described with reference to FIG. 8. FIG. 8 is a schematic view for illustrating the forging lines of the preform 13 a′ after the forging of this embodiment. Ends of forging lines K are focused in a range of the recessed portion 52, and hence a central segregated portion J is also fastened in the recessed portion 52. Thus, the central segregated portion J does not appear on the joining end surface, and hence an outer joint member of a constant velocity universal joint having satisfactory strength of a welded portion and satisfactory quality is obtained.

Now, the characteristic condition of the forging step S2 s of this embodiment found through the evaluation test is described below.

[Upset Processing Limit]

An upset processing limit is evaluated based on a ratio of an upset distance L and a blank diameter Dw. That is, as a parameter for determining the upset processing limit, an upset ratio L/Dw that is a ratio of the upset distance L and the blank diameter Dw is desired. When the upset ratio L/Dw is large, buckling occurs, and roll-in of a surface and the like occur, with the result that normal forging cannot be performed.

In a drive shaft for automobiles to which the shaft member of this embodiment is applied, the billet 13 a″ cut from a bar material has a diameter of from about 30 mm to about 50 mm, and the joining end portion of the preform 13 a′ after the forging has a diameter Dw3 of from about 40 mm to about 60 mm. Regarding the shaft member having such dimensions, the following has been confirmed. When an upset distance in the preforming step is represented by L1, and a diameter of the billet 13 a″ that is a blank is represented by Dw1, and when an upset distance in the main forming step is represented by L2, and a diameter of the preformed product 13 a′1 that is a blank is represented by Dw2, as safe upset ratios that do not cause bucking even when the heating temperature of the blank is set to from 800° C. to 1,000° C., the upset ratio L1/Dw1 in the preforming step is set to L1/Dw1<1.5, and the upset ratio L2/Dw2 in the main forming step is set to L2/Dw2<0.5.

Now, the diameter Dw2 of the preformed product 13 a″ is described. The punch 121 in the preforming step has the tapered forming surface 121 a. Therefore, when preforming is performed, the preformed product 13 a″1 increases in diameter up to a state following the part (connected portion 120 e side) of the second step portion forming surface 120 c of the die 120 and is gently tapered from the diameter increased portion toward the punch 121 side, as illustrated in FIG. 6a . Therefore, the diameter Dw2 of the preformed product 13 a″1 is defined as a diameter obtained by averaging the minimum diameter Dw2′ and the maximum diameter Dw2″ of the conical portion illustrated in FIG. 6b . That is, Dw2−(Dw2′+Dw2″)/2 is satisfied.

[Shape of Punch in Preforming Step]

When the heating temperature of the blank is from about 800° C. to about 1,000° C., deformation resistance increases as compared to the hot region, and buckling is liable to occur. It has also been found that cylindrical upsetting is more liable to cause bucking as compared to conical upsetting. Therefore, the forming surface 121 a of the punch 121 in the preforming step is tapered, and an optimum conical angle θ in this case is set to 5°≤θ≤20°.

[Upset Distance in Main Forming Step]

The findings in the course of development are illustrated in FIG. 9. It has been found that, when upset distance L2 for each time is 20 mm or less in the main forming step, forming by forging is completed before a corner is filled with the material, and hence insufficient filling H occurs. It has also been found that, as illustrated in FIG. 7, when a step difference between the minimum diameter Dw2′ of the preformed product 13 a′1 and the diameter Dw3 of the substantially cylindrical forming surface 123 a of the punch 123 in the main forming step is represented by G, and the step difference G (=Dw3−Dw2′) is 10 mm or more, mold release of the material is caused, and a sink I (see FIG. 9) occurs. Thus, the amount of the upset distance L2 for each time in the main forming step was set to 25 mm or more, and the step difference G between the minimum diameter Dw2′ of the preformed product 13 a″1 and the diameter Dw3 of the substantially cylindrical forming surface 123 a of the punch 123 was set to 9 mm or less.

Under the above-mentioned forging condition, the preform 13 a′ had JIS grain size Nos. 6 to 8 in the step portion 54 (portion in which the joining end surface is formed), the second step portion 55, and the first step portion 56 being the processed portions, and thus, the grain size equal to or more than that of the blank was able to be maintained. Further, in the unprocessed portion adjacent to the first step portion 56, the preform 13 a′ had JIS grain size Nos. 5 to 6, and thus slight growth of a grain size by heating was observed. However, such slight growth was at the level of causing no practical problem. The preform in the unheated portion had JIS grain size Nos. 6 to 7.

As described above, the forging step S2 s for the shaft member of this embodiment enabled forging in the temperature region of from about 800° C. to about 1,000° C. lower than the hot region. Thus, the enlargement of a crystal grain was suppressed, and forging without generation of an oxide film was able to be achieved. With this, the normalizing step and the shot-peening processing after the forging were able to be omitted to reduce the manufacturing cost.

In the forging step S2 s for the shaft member of this embodiment described above, upset forging using an upsetter is illustrated. However, the present invention is not limited thereto, and similar processing can be performed through use of a screw press (Vincent-type screw press) or the like.

Next, to summarize the manufacturing concept, standardization of a product type of the cup member is additionally described while exemplifying a shaft member having a product number different from that of the above-mentioned shaft member 13 a of the long stem type illustrated in FIG. 5. A shaft member 13 b illustrated in FIG. 12 and FIG. 13 is used as a general stem type on the inboard side. The shaft member 13 b has the joining end surface 51 to be brought into abutment against the joining end surface 50 (see FIG. 4b ) of the bottom portion 12 a 2 (projecting portion 12 a 3) of the cup member 12 a. The outer diameter B and the inner diameter E of the joining end surface 51 are set to the equal dimensions to the outer diameter B and the inner diameter E of the joining end surface 51 of the shaft member 13 a of the long stem type illustrated in FIG. 5.

The shaft member 13 b is used as the general stem type on the inboard side. Accordingly, the shaft member 13 b comprises a shaft section with a small length, and a sliding bearing surface 18 formed on an axial center portion thereof, and a plurality of oil grooves 19 are formed in the sliding bearing surface 18. The spline Sp and a snap ring groove 48 are formed in an end portion of the shaft member 13 b on the side opposite to the cup member 12 a side. As described above, even when there are differences in types, such as the general length stem type and the long stem type, and shaft diameters and outer peripheral shapes vary in each vehicle type, the diameter B of the joining end surface 51 of the shaft member 13 a or 13 b is set to an equal dimension.

The outer diameter B of the joining end surface 50 of the cup member 12 a and the joining end surface 51 of the shaft member 13 a or 13 b is set to an equal dimension for each joint size. Thus, the cup member prepared for common use for each joint size, and the shaft member having a variety of specifications of the shaft section for each vehicle type can be prepared in a state before heat treatment. Further, the intermediate component of each of the cup member 13 a and the shaft member 13 a or 13 b can be assigned with a product number for management. Even when standardizing product types of the cup member 12 a, various types of the outer joint members 11 satisfying requirements can be produced quickly through combination of the cup member 12 a and the shaft member 13 a or 13 b having a variety of specifications of the shaft section for each vehicle type. Therefore, standardization of a product type of the cup member 12 a can reduce cost and alleviate a burden of production management.

The standardization of the product type of the cup member is described above by taking the differences in types, such as the general length stem type and the long stem type, as an example for easy understanding, but the present invention is not limited thereto. The same applies to standardization of the product type of the cup member for shaft members having a variety of specifications of the shaft section for each vehicle type among the general length stem types, and for shaft members having a variety of specifications of the shaft section for each vehicle type among the long stem types.

As a summary of the above description, FIG. 14 is a diagram for illustrating an example of standardization of a product type of the cup member according to this embodiment. As illustrated in FIG. 16, the cup member is prepared for common use for one joint size, and is assigned with, for example, a product number C001 for management. In contrast, the shaft member has a variety of specifications of the shaft section for each vehicle type, and is assigned with, for example, a product number S001, S002, or S(n) for management. For example, when the cup member assigned with the product number C001 and the shaft member assigned with the product number S001 are combined and welded to each other, the outer joint member assigned with a product number A001 can be produced. Thus, owing to standardization of a product type of the cup member, it is possible to reduce cost and to alleviate a burden of production management. In the standardization of a product type, the cup member is not limited to one type for one joint size, that is, not limited to one type assigned with a single product number. For example, the cup member comprises cup members of a plurality of types (assigned with a plurality of product numbers, respectively) that are prepared for one joint size based on different specifications of a maximum operating angle, and are each prepared so that the outer diameter B of the joining end surface of each of those cup members has an equal dimension.

A modified example of the outer joint member according to the first embodiment is described with reference to FIG. 15. FIG. 15 is a vertical sectional view for illustrating a cup member before welding. In this modified example, the form of the joining end surface of the cup member of the first embodiment is different. As illustrated in FIG. 15, a joining end surface 50 ₁ formed on a bottom portion 12 a 2 ₁ and a projecting portion 12 a 3 ₁ of a cup member 12 a ₁ is subjected to turning up to the center in a radial direction. This is an example in which turning allowance after the forging is large. The portions having the same functions as those of the first embodiment are denoted by the same reference symbols (excluding subscripts). Other features and advantages, that is, details of the overview of the respective steps, the states of the cup member and the shaft member in the main processing steps, the forging step for the shaft member, the preparation of the cup member for common use, the welding method, the standardization of the product type, the configuration of the outer joint member, and the like as described above in the first embodiment on the manufacturing method are the same as those of the first embodiment. Therefore, all the details of the first embodiment are applied in this embodiment to omit redundant description.

FIG. 16 is an illustration of a manufacturing method according to a second embodiment of the present invention. In the manufacturing steps of this embodiment, the heat treatment step for the cup member, which is involved in the heat treatment step S7 in FIG. 3 as described above in the first embodiment, is provided before the welding step S6 in the sequence and named “heat treatment step S5 c”, to thereby prepare the cup member as a finished product. Details of other aspects of the second embodiment than this aspect, that is, details of the overview of the respective steps, the states of the cup member and the shaft member in the main processing steps, the forging step for the shaft member, the preparation of the cup member for common use, the welding method, the standardization of the product type, the configuration of the outer joint member, and the like as described above in the first embodiment on the manufacturing method are the same as those of the first embodiment. Therefore, all the details of the first embodiment are applied in this embodiment, and only the difference is described.

As illustrated in FIG. 4b , the cup member 12 a has a shape extending from the joining end surface 50 to the large-diameter cylindrical portion 12 a 1 via the bottom portion 12 a 2, and the portions to be subjected to heat treatment that involves quenching and tempering are the track grooves 30 and the cylindrical inner peripheral surface 42 located at the inner periphery of the cylindrical portion 12 a 1. Therefore, the cup member 12 a generally has no risk of thermal effect on the heat-treated portion during the welding. For this reason, the cup member 12 a is subjected to heat treatment before the welding to be prepared as a finished component. The manufacturing steps of this embodiment are suitable in practical use.

In the manufacturing steps of this embodiment, the cup member 12 a is subjected to heat treatment for preparing the cup member 12 a as a finished product, and is therefore assigned with a product number indicating a finished product for management. Thus, the standardization of the product type of the cup member 12 a remarkably reduces the cost and alleviates the burden of production management. Further, the cup member 12 a can be manufactured solely until the cup member 12 a is completed as a finished product through the forging, turning, and heat treatment. Thus, the productivity is enhanced by virtue of reduction of setups and the like as well.

In this embodiment, in FIG. 14 for illustrating the example of standardization of the product type of the cup member as described above in the first embodiment, only the product number of the cup member in FIG. 16 is changed to the product number indicating a finished product, whereas the product numbers of the shaft member and the outer joint member are the same as those of the first embodiment. Therefore, description thereof is omitted herein.

FIG. 17 is an illustration of a manufacturing method according to a third embodiment of the present invention. In the manufacturing steps of this embodiment, the heat treatment steps for the cup section and the shaft section, which are involved in the heat treatment step S7 in FIG. 3 as described above in the first embodiment, and the grinding step S8 for the shaft section in FIG. 3 are provided before the welding step S6 in the sequence and named “heat treatment step S5 c for cup member”, “heat treatment step S5 s for shaft member”, and “grinding step S6 s”. Thus, both the cup member and the shaft member are prepared as finished products. Details of other aspects of the third embodiment than this aspect, that is, details of the overview of the respective steps, the states of the cup member and the shaft member in the main processing steps, the forging step for the shaft member, the preparation of the cup member for common use, the welding method, the standardization of the product type, the configuration of the outer joint member, and the like as described above in the first embodiment on the manufacturing method are the same as those of the first embodiment. Therefore, all the details of the first embodiment are applied in this embodiment, and only the difference is described.

After the spline processing step S4 s, a hardened layer having a hardness of approximately from 50 HRC to 62 HRC is formed in a predetermined range of the outer peripheral surface of the shaft member by induction quenching in the heat treatment step S5 s. Heat treatment is not performed on a predetermined portion in the axial direction, which includes the joining end surface 51. The heat treatment for the cup member, the assignment of the product number, and the like are the same as those of the second embodiment on the manufacturing method, and redundant description is therefore omitted herein.

After the heat treatment step S5 s, the shaft member is transferred to the grinding step S6 s so that the bearing mounting surface 14 and the like are finished. Thus, the shaft member is obtained as a finished product. Then, the shaft member is assigned with a product number indicating a finished product for management. The manufacturing steps of this embodiment are suitable in a case of a cup member and a shaft member having shapes and specifications with no risk of thermal effect on the heat-treated portion during the welding.

In the manufacturing steps of this embodiment, both the cup member and the shaft member can be assigned with product numbers indicating finished products for management. Thus, the standardization of the product type of the cup member further remarkably reduces the cost and alleviates the burden of production management. Further, the cup member and the shaft member can be manufactured independently of each other until the cup member and the shaft member are completed as finished products through the forging, turning, heat treatment, grinding after heat treatment, and the like. Thus, the productivity is further enhanced by virtue of reduction of setups and the like as well.

In this embodiment, in FIG. 14 for illustrating the example of standardization of the product type of the cup member as described above in the first embodiment, the product numbers of the cup member and the shaft member in FIG. 16 are changed to the product numbers indicating finished products. The product number of the outer joint member is the same as that of the first embodiment. Therefore, description thereof is omitted herein. Note that, the cup member and the shaft member to be prepared as finished components are not limited to the cup member and the shaft member subjected to finishing such as the above-mentioned grinding after heat treatment or cutting after quenching, but encompass a cup member and a shaft member in a state in which the heat treatment is completed while the finishing is uncompleted.

As described in the standardization of the product type, the cup member is not limited to one type for one joint size, that is, not limited to one type assigned with a single product number. Specifically, as described above, the cup member encompasses, for example, cup members of a plurality of types (assigned with a plurality of product numbers, respectively) that are prepared for one joint size based on different specifications of a maximum operating angle, and are also prepared so that the outer diameters B of the above-mentioned joining end surfaces of the cup members are set to equal dimensions. In addition, the cup member encompasses, for example, cup members of a plurality of types (assigned with a plurality of product numbers, respectively) that are prepared for one joint size in order to achieve management of the cup members in a plurality of forms including intermediate components before heat treatment and finished components in consideration of the joint function, the circumstances at the manufacturing site, the productivity, and the like, and are also prepared so that the outer diameters B of the above-mentioned joining end surfaces of the cup members are set to equal dimensions.

Next, an outer joint member according to a second embodiment of the present invention is described with reference to FIG. 18 and FIG. 19. In this embodiment, parts that have the same function as those of the outer joint member according to the first embodiment are denoted by the same reference symbols (excluding subscripts), and only main points are described.

A plunging type constant velocity universal joint 102 illustrated in FIG. 18 is a tripod type constant velocity universal joint (TJ), and comprises an outer joint member 11 ₂ comprising a cup section 12 ₂ and the long stem section 13 that extends from a bottom portion of the cup section 12 ₂ in the axial direction, an inner joint member 16 ₂ housed along an inner periphery of the cup section 12 ₂ of the outer joint member 11 ₂, and rollers 19 serving as torque transmitting elements that are arranged between the outer joint member 11 ₂ and the inner joint member 16 ₂. The inner joint member 16 ₂ comprises a tripod member 17 comprising three equiangular leg shafts 18 on which the rollers 19 are externally fitted.

Similarly to the outer joint member according to the first embodiment, the inner ring of the support bearing 6 is fixed to the outer peripheral surface of the long stem section 13, and the outer ring of the support bearing 6 is fixed to the transmission case with the bracket (not shown). The outer joint member 11 ₂ is supported by the support bearing 6 in a freely rotatable manner, and thus the vibration of the outer joint member 11 ₂ during driving or the like is prevented as much as possible.

FIG. 19 is a partial vertical sectional view for illustrating the outer joint member 11 ₂. As illustrated in FIG. 22, the outer joint member 11 ₂ comprises a bottomed cylindrical cup section 12 ₂ that is opened at one end and has inner peripheral surfaces 31 ₂ and the track grooves 30 ₂, on which the rollers 19 (see FIG. 18) are caused to roll, formed at three equiangular positions on an inner peripheral surface of the cup section 12 ₂, and the long stem section 13 that extends from a bottom portion of the cup section 12 ₂ in the axial direction and comprises the spline Sp serving as the torque transmitting coupling portion formed at the outer periphery of the end portion on the opposite side to the cup section 12 ₂ side. The outer joint member 11 ₂ is formed by welding the cup member 12 a ₂ and the shaft member 13 a to each other.

As illustrated in FIG. 19, the cup member 12 a ₂ is an integrally-formed product having a cylindrical portion 12 a 1 ₂ and a bottom portion 12 a 2 ₂. The cylindrical portion 12 a 1 ₂ has the track grooves 30 ₂ and the inner peripheral surfaces 31 ₂ formed at the inner periphery thereof. A projecting portion 12 a 3 ₂ is formed at the bottom portion 12 a 2 ₂ of the cup member 12 a ₂. The boot mounting groove 32 is formed at an outer periphery of the cup member 12 a ₂ on the opening side thereof. The bearing mounting surface 14 and the snap ring groove 15 are formed at the outer periphery of the shaft member 13 a on the cup member 12 a ₂ side, whereas the spline Sp is formed at the end portion on the opposite side to the cup member 12 a ₂ side.

A joining end surface 50 ₂ formed at the projecting portion 12 a 3 ₂ of the bottom portion 12 a 2 ₂ of the cup member 12 a ₂ and the joining end surface 51 formed at the end portion of the shaft member 13 a on the cup member 12 a ₂ side are brought into abutment against each other, and are welded to each other by electron beam welding performed from the radially outer side. The welded portion 49 is formed of a bead, which is formed by a beam radiated from the radially outer side of the cup member 12 a ₂. Similarly to the outer joint member of the first embodiment, the outer diameters B of the joining end surface 50 ₂ and the joining end surface 51 are set to equal dimensions for each joint size. The welded portion 49 is formed on the joining end surface 51 located on the cup member 12 a ₂ side with respect to the bearing mounting surface 14 of the shaft member 13 a, and hence the bearing mounting surface 14 and the like can be processed in advance so that post-processing after welding can be omitted. Further, due to the electron beam welding, burrs are not generated at the welded portion. Thus, post-processing for the welded portion can also be omitted, which can reduce the manufacturing cost.

The details of the outer joint member according to this embodiment are the same as the details of the outer joint member according to the first embodiment, and the manufacturing method according to the first to third embodiments as described above. Therefore, all of those details are applied in this embodiment to omit redundant description.

In the above-mentioned embodiments and the above-mentioned modified examples, the case to which electron beam welding is applied is described, but laser welding is also similarly applicable.

In the outer joint member according to the embodiments and the modified examples described above, the cases where the present invention is applied to the double-offset type constant velocity universal joint as the plunging type constant velocity universal joint 10, and to the tripod type constant velocity universal joint as the plunging type constant velocity universal joint 10 are described. However, the present invention may be applied to an outer joint member of another plunging type constant velocity universal joint such as a cross-groove type constant velocity universal joint, and to an outer joint member of a fixed type constant velocity universal joint. Further, in the above, the present invention is applied to the outer joint member of the constant velocity universal joint, which is used to construct the drive shaft. However, the present invention may be applied to an outer joint member of a constant velocity universal joint, which is used to construct a propeller shaft.

The present invention is not limited to the above-mentioned embodiments and the above-mentioned modified examples. As a matter of course, various modifications can be made thereto without departing from the gist of the present invention. The scope of the present invention is defined in Claims, and encompasses equivalents described in Claims and all changes within the scope of claims.

DESCRIPTION OF REFERENCE SIGNS

-   -   1 drive shaft     -   2 intermediate shaft     -   3 spline     -   4 boot     -   5 boot     -   6 support bearing     -   10 plunging type constant velocity universal joint     -   11 outer joint member     -   12 cup section     -   12 a cup member     -   12 a 1 cylindrical portion     -   12 a 2 bottom portion     -   13 long shaft section     -   13 a shaft member     -   13 a″ billet     -   13 a′ preform     -   14 bearing mounting surface     -   16 inner joint member     -   17 tripod member     -   19 torque transmitting element (roller)     -   20 fixed type constant velocity universal joint     -   21 outer joint member     -   22 inner joint member     -   23 torque transmitting element (ball)     -   24 cage     -   30 track groove     -   31 inner peripheral surface     -   40 track groove     -   41 torque transmitting element (ball)     -   42 cylindrical inner peripheral surface     -   49 welded portion     -   50 joining end surface     -   51 joining end surface     -   52 recessed portion     -   54 step portion     -   100 welding apparatus     -   101 electron gun     -   108 case     -   109 vacuum pump     -   111 sealed space     -   120 die     -   121 punch     -   122 die     -   123 punch     -   B outer diameter     -   Dw1 diameter     -   Dw2 diameter     -   Dw3 diameter     -   E inner diameter     -   J central segregated portion     -   K forging line     -   L upset distance     -   L1 upset distance     -   L2 upset distance     -   O joint center     -   O1 curvature center     -   O2 curvature center     -   Sp spline     -   θ conical angle 

The invention claimed is:
 1. A method of manufacturing an outer joint member of a constant velocity universal joint, which is constructed by forming, through use of separate members, a cup section having track grooves formed at an inner periphery of the cup section and engageable with torque transmitting elements, and a shaft section formed at a bottom portion of the cup section, and by welding a cup member forming the cup section and a shaft member forming the shaft section, the method comprising: preparing the cup member of carbon steel, the preparing of the cup member including forging to integrally form a cylindrical portion and a bottom portion, and machining a joining end surface at an outer surface of the bottom portion after the forging; preparing the shaft member of carbon steel, the preparing of the shaft member including a preforming step of forging a billet cut from a bar material to form a tapered shape at a portion of the billet, a main forming step of forging, at the portion of the billet having the tapered shape, a step portion and a radially inner side recessed portion at the step portion, and a machining step of machining a joining end surface at the step portion, the joining end surface of the shaft member to be joined to the bottom portion of the cup member; bringing the joining end surface of the cup member and the joining end surface of the shaft member into abutment against each other; welding the cup member and the shaft member by radiating a beam from an outer side of the cup member to an abutment portion between the cup member and the shaft member in a radial direction of the cup member; and forming the outer joint member.
 2. The method of manufacturing an outer joint member of a constant velocity universal joint according to claim 1, wherein, in the preparing of the cup member, the machining comprises machining the joining end surface of the cup member with an outer diameter having a constant shape.
 3. The method of manufacturing an outer joint member of a constant velocity universal joint according to claim 1, wherein, in the preparing of the shaft member, a radio L2Dw2, where L2 is an upset distance in the main forming step and Dw2 is a diameter obtained by averaging a minimum diameter of the portion of the billet having the tapered shape and a maximum diameter of the portion of the billet having the tapered shape after the preforming step, is set to be smaller than a ratio of L1/Dw1, where L1 is an upset distance in the preforming step and Dw1 is an original diameter of the billet.
 4. The method of manufacturing an outer joint member of a constant velocity universal joint according to claim 1, wherein, in the prefroming step, the forging comprises using a punch having a conical angle (θ) of from 5° to 20° to form the tapered shape at the portion of the billet.
 5. The method of manufacturing an outer joint member of a constant velocity universal joint according to claim 1, wherein the preparing of the shaft member further includes heating the billet to from 800° C. to 1,000° C.
 6. A method of manufacturing an outer joint member of a constant velocity universal joint, which is constructed by forming, through use of separate members, a cup section having track grooves formed at an inner periphery of the cup section and engageable with torque transmitting elements, and a shaft section formed at a bottom portion of the cup section, and by welding a cup member forming the cup section and a shaft member forming the shaft section, the method comprising: providing the cup; preparing the shaft member of carbon steel, the preparing of the shaft member including a preforming step of forging a billet cut from a bar material to form a tapered shape at a portion of the billet, a main forming step of forging, at the portion of the billet having the tapered shape, a step portion and a radially inner side recessed portion at the step portion, and a machining step of machining a joining end surface at the step portion, the joining end surface of the shaft member to be joined to the cup member; bringing a joining end surface of the cup member and the joining end surface of the shaft member into abutment against each other; welding the cup member and the shaft member by radiating a beam from an outer side of the cup member to an abutment portion between the cup member and the shaft member in a radial direction of the cup member, and forming the outer joint member. 